Magnetooptic media has been used for storing digital data and analog data in digital forms. Many current day recording systems encode data using a (2,7) run length limited (RLL) modulation code and store the encoded data on the disk using pulse position modulation (PPM). PPM recording on magnetooptic media is achieved by writing magnetic domains, marks, of a certain polarity to the disk for each 1 in the encoded data. No mark is written for a 0. When the record is read by scanning over the data with a laser beam, the written marks will rotate the polarization of the laser beam differently then when the laser beam is scanning over parts of the record where no marks are written. Thus by detecting the polarization rotation of the laser beam, a readback signal is produced. Each mark will produce a signal peak in the readback signal. The highest density patterns of the encoded data, when stored to the disk at high linear densities, result in undesired intersymbol interference (ISI). ISI occurs when the encoded data has two 1s separated by the minimum number of 0s. For the (2,7) RLL code the minimum number of 0 corresponds to the d constaint of the code, 2. The effect of such ISI in PPM is to move the peaks of the readback signal closer together. Also, the valley between the two peaks will be higher then the valleys corresponding to a longer string of 0s. The readback signal is converted to an asynchronized logic stream (ASYNC DATA) by a peak detector which produces a pulse for each peak of sufficient amplitude in the readback signal. The ASYNC DATA is input to a synchronizer which uses a phase locked loop (PLL). The leading edge (LE) of ASYNC DATA pulses into the synchronizer should nominally occur centered in the clock cells of the synchronizer to allow for the most margin in data synchronization The peak movement produced by ISI results in the LEs of the two pulses in the ASYNC DATA being moved closer together. This moves the LEs out of the center of the clock cell of the synchronizer and can be regarded as a phase error. Such phase error in the ASYNC DATA, coupled with the timing jitter produced by noise on the readback signal into the peak detector, coupled with imperfect mark formation due to defects in (and non-uniformity of) the magnetooptic media, can result in movement of the LEs of ASYNC DATA pulses out of the proper clock cell and into the next, producing an error in the data out of the synchronizer. Additionally, noise on the readback signal and media defects can produce false signal peaks. This is particularly true in the shallow valleys between peaks written at the minimum spacing due to the high density patterns in the encoded data stream. Another mechanism in PPM magnetooptic recording that can produce errors is thermal interaction effects when marks are being written. Marks are written by heating the magnetooptic media with a laser beam above the Curie temperature while applying a magnetic field which has a polarity opposite that of the media before heating. When the laser power is reduced, the temperature of the magnetooptic media drops below the Curie temperature and the magnetization of the written mark is frozen at the magnetic polarity of the applied magnetic field, opposite of the surrounding media which did not exceed the Curie temperature. When two marks are written sequentially close together, the media heating produced by the formation of the first mark has not totally dissipated when the second mark is being formed. This dissipation of the heat from the formation of the first mark forms a thermal gradient as the heat flows away from the first mark. When the second mark is being formed, the media will heat more readily in the direction towards the first mark. Thus the mark formation will not be symmetric, but will instead tend to grow towards the first mark. The peak of the readback signal corresponds to the center of the written mark. Thus, aside from ISI, the peak corresponding to the second written mark will shift towards the first. Like ISI, this problem manifests itself most noticeably at the high density patterns of the encoded data stream. The three effects discussed (ISI induced peak shift, false peak detection in the valley between two peaks, and thermal interaction between written marks) are all much worse for the highest density pattern (corresponding to two 1s separated by two 0s in the case of a (2,7) RLL code) then for any other. In particular, the second peak of an isolated 1001 pattern for a (2,7) code is troublesome due to the shallow slope of the readback signal in the leading part of the clock cell. As a result, a major failure mechanism at high linear recording densities is for the second peak on the readback signal corresponding to a high density pattern to be detected as having occurred early (e.g. when 1001000 is recorded but a 1010000 is clocked out of the data synchronizer on readback). For the case when two high density patters are adjacent, most ISI will cancel for the middle 1, though the other two effects still contribute to misdetection (i.e. a 1001001 being detected as a 10100001). Both of the aforementioned failure mechanisms result in a written 01 being read as a 10 and can be called a bit swapping error. Depending on the read detector design, false peaks in the shallow valleys between peaks corresponding to the high density patterns can also be manifested by an 0 being detected as a 1 (i.e. a 1001 being detected as a 1011, 1101 or a 1111). This could be called an extra 1 error. In addition to the errors induced in the synchronized data, these failure mechanisms produce erroneous phase information to the PLL which shift the phase of the clock. When the PLL clock is shifted by an erroneous phase update, the detection margin is affected until proper phase lock is reacquired. Proper synchronization is required to define the boundaries of the (d,k) code symbol groups. If the PLL is severely affected bit slip or loss of phase lock may occur. Bit slip (the synchronizer gaining or losing one clock cycle) can result in erroneous data until the decoder reacquires synchronization at a resync feature; loss of phase lock can result in loss of the rest of the record. It is desired that bit swapping and extra 1s be prevented so that errors in the synchronized data and the resultant possibility of bit slip and loss of phase lock be avoided. It is also desired that the extra 1s and bit swapping be prevented in the variable frequency oscillator (VFO) field at the beginning of the record before data as this can cause the PLL to take longer to acquire phase lock and detect that phase lock has occurred. Correction of these failure mechanisms allows the PLL to become slaved to the phase of the LEs of the ASYNC DATA pulses more quickly. Also, by preventing these failure mechanisms, the readback reliability is increased and sensitivity of the readback circuits to noise and ISI is greatly reduced.